[unreadable] A major limitation in the development of effective treatment for dementia has been poor understanding of the relationship between neuronal transmission and behavior. This study will use arterial spin labeled perfusion MRI (ASL-pMRI) to measure changes in regional cerebral blood flow (rCBF) following acute and chronic administration of cholinesterase inhibitors (ChEI) in diffuse Lewy body dementia. Simultaneous high resolution structural imaging and contemporary neuropsychological assessments will be obtained. From this a relationship between cognitive performance and changes in rCBF can be defined. Additionally, combined structural and perfusion MRI will provide information that may predict clinical response to ChEI. The trial will include two phases, first, a double-blind, randomized, crossover, placebo-controlled trial to measure the effects of a single oral dose of ChEI on cognitive function and rCBF. The second phase will be an open labeled, prospective study to assess the chronic effects of ChEI administered over a period of three months. [unreadable] [unreadable]